The present invention relates to a character recognition system for an optical document reader and more specifically to a low cost terminal oriented document reader provided with a low speed character recognition system.
Modern information processing systems often include a plurality of remotely located terminal units attached to a central processing system. An example of such terminal units are cheque readers used in various banking systems. Such readers may be used in large numbers for direct customer service and need therefore to be of low cost type, however, the processing speed is often not critical.
An example of such a banking terminal cheque reader is described in U.S. Pat. No. 4,239,151, issued Dec. 16, 1980 to Enser et al disclosing a low cost low speed magnetic bar code reader system for a CMC7 code. In this system data detected by a read head is stored in a buffer and a slow micro processor is used to recognize characters asynchronously as compared to the read operation.
A similar system for an optical reader used to recognize OCR characters is disclosed in the U.S. Pat. No. 4,447,774 to Edlund et al. In this system the detected video data from the document is buffered in compressed form in a memory for subsequent recognition use. A useful low cost video detector device for such a system is disclosed in the U.S. Pat. No. 4,426,731 (to Stalberg). This video detector device discloses a threshold adjusting system including compensating means for compensating for variations in the read video signals.
In some applications the documents to be read might include two or more fields of different character codes. IBM Technical Disclosure Bulletin Vol. 23, No. 8, Jan. 19, 1981, pages 3613 and 3614 discloses a multicode scanner capable of reading such fields on a document. This scanner comprises a common analog to digital converter and a plurality of parallel computers, one for each code to be recognized. This is a rather expensive system requiring sophisticated circuits for signal detection and processing.
A specific problem encountered in an optical multicode reader where detected signals are buffered before recognition, is the difficulty of applying an appropriate threshold level for each code type. This is especially important if some noise prints such as stamps occur on the code line to be read.